The present invention relates to a gasket and a pipe joint comprising the gasket.
Pipe joints are widely used, for example, in fluid control devices for use in fabricating semiconductors. Such pipe joints comprise a pair of tubular joint members, an annular gasket interposed between opposed end faces of the two joint members, and threaded means for joining the two joint members. With pipe joints of the type described, it is common practice to prepare the tubular joint members and the gasket from the same stainless steel (e.g., SUS316L). When checked for Vickers hardness, the joint members had a hardness of about 310 to about 390 Hv at the surface and about 260 to about 320 Hv at a portion thereof 100 micrometers away from the surface, and the gasket had a hardness of about 300 to about 330 Hv at the surface and about 260 to about 290 Hv in its interior.
Since pipe joints are repeatedly disassembled and reassembled for the maintenance and inspection of the fluid control device, the conventional pipe joint wherein the tubular joint members and gasket are made of the same stainless steel has the problem that the joint members which are difficult to replace unlike the gasket develop flaws, failing to assure the joint of fluid tightness. Although it is possible to change the material for the gasket from stainless steel to nickel or copper which is softer, another problem is then encountered in that the material reacts with the gas for use in fabricating semiconductors. For example, Ni reacts with CO at room temperature, producing Ni carbonyl [Ni(CO).sub.4 ] gas, resulting in impaired fluid tightness due to the corrosion of Ni or reducing the purity of the gas to be used for manufacturing semiconductors.